Problem: In geometry class, the girl to boy ratio is $3$ to $5$. If there are a total of $32$ students, how many girls are there?
A ratio of $3$ girls to $5$ boys means that a set of $8$ students will have $3$ girls and $5$ boys. A class of $32$ students has $4$ sets of $8$ students. Because we know that there are $3$ girls in each set of $8$ students, the class must have $4$ groups of $3$ girls each. There is a total of $12$ girls in geometry class.